Structure, EPR and UV–VIS and IR spectroelectrochemistry of reversibly reducible compounds [(C5Me5)IrCl(L)](PF6), L = 1,3-dimethyllumazine or 1,3-dimethylalloxazine
摘要:
In an attempt to model possible metal-pterin or metaI-flavin ligand interactions the title compounds have been prepared and their structure, spectroscopy and spectroelectrochemistry (EPR, IR, UV-VIS) compared with results for the corresponding rhodium analogues. The X-ray crystal structure of [(C(5)Me(5))IrCl(DML)](PF6), DML = 1,3-dimethyllumazine, shows O-4/N-5 chelate coordination of iridium with a shorter bond to the nitrogen centre [2.103(4) vs. 2.186(3) Angstrom], a slightly more unsymmetrical situation than that found in the rhodium analogue. Electrochemical studies (cyclic voltammetry, polarography) showed largely reversible one-electron reduction processes to radical species [(C(5)Me(5))IrCl(L)](.) which allowed us to investigate the EPR, IR and UV-VIS response to the reduction. Although the EPR spectra of the iridium compounds remained unresolved, the low g factors (g < 2) and particular line shapes revealed small but significant contributions from the heavy-metal centre. Long-wavelength absorptions at ca. 600 nm and low-energy shifts of the carbonyl stretching bands confirm the formulation [(C(5)Me(5))(IrCl)-Cl-III(L(-1))](.) for the electronic situation.